This invention relates to a method of avoiding interferences which cause false-positive fecal occult blood determinations in stool samples when employing a method based on the reaction of guaiac with hemoglobin.
The avoidance of a false-positive test has, in the past, often relied on control of the dietary intake of the patient, when tests which rely on guaiac-peroxidase reagents are applied. An improved method of applying such tests is described in U.S. Pat. No. 4,333,734 by the same inventor hereof, wherein false-positive tests, due to the presence of peroxidase from ingested foods, are avoided. The basis of this method is a combination of the partial denaturing of peroxidase enzymes and the removal of necessary metals for efficient peroxidase enzyme activity. This combination of actions eliminates the interfering effect of peroxidase without requiring extreme conditions that might effect hemoglobin reactively.
During extensive clinical testing of the method and device of U.S. Pat. No. 4,333,734, it has been found that certain of the samples taken from patients still produce false-positive tests. It is believed that these false positive tests may be caused by drugs or drug metabolites, or a large variation in pH in the excrement of the patients.
The present invention has as its primary object the reduction or elimination of false-positive tests which occur due to interfering drug or drug metabolites when using the guaiac-peroxidase type reaction scheme for determination of hemoglobin in various samples.